Telegraph system



Nov 12, 1940. G, l HARMS 2,221,136

TELEGRAPH SYSTEM Filed Feb. l, 1939' ATTO RN EY Patented Nov. 12, 1940 UNITED s'rTas Gordon .lohn Harm,

to mcriean 'E' l e ppiication Feci.

iii illfi This invention relates to telegraph circuits and systems. More particularly, this invention is 1 intended to provide arrangements for reducing or eliminating signal distortion in telegraph systems. In neutral telegraph systems signals may be transmitted under the control of a relay the armature and :marking contact oi which are ar ranged to close the, line or loop so as to cause current to dow and thus produce a marking pulse, and to interrupt the current flow or open the circuit to produce a. spacing pulse. To reduce sparking at the contacts o! the relay as its arma= .ture travels back and forth interrupting the line circuit, a so-called spark-killer is usually employed, the spark-killer comprising a resistor and condensed connected in series with each other between vthe armature and the marking contact of the relay. As the armature leavesthe latter' contact, the condenser becomes charged and remains charged until the armature later returns to that contact at which time the condenser becomes discharged through the resistor.

In such neutral telegraph systems, the circuit has a finite impedance when the circuit is closed for producing the marking pulse; but the imm pedance of the circuit is increased considerably, to an infinite value for direct current, when the line circuit is opened for producing the spacing pulse. Thus the impedance of the circuit is variable between two widely diferent values during signaling. These circuit impedance changes cause the growth of current at closure to differ from the decay at opening and this results in lengthening of one of the pulses relative to the other, as is well known.

The average lengthening of one of the pulses relative to the other is a type of distortion called "signal bias. This may be so large due to the circuit characteristics as to seriously affect transmission quality.

It is an object of this invention to reduce or eliminate signal bias in telegraph transmission over circuits 4of the type referred to.

It is another object of this invention to produce well-defined signals in neutral telegraph systems by reducing or eliminating distortion.

These and other objects of the invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing in which Figure 1 shows schematically a telegraph circuit broadly illustrating the features of this invention and Fig. 2 shows a telegraph circuit suitable for two-way transmission.

Fig. 1 of the drawing shows a schematic of a form of neutral telegraph circuit to which the invention has been applied merely for purposes of illustration. The circuit comprises battery B1, :conductor L1, the contact M and of a 4spark-killer circuit.

@FUSE T, the line conductor Lz with its ffy Cc (shown in dotted lines),

These form the so-called The Winding W of relay T may be connected to a battery B3 and a key K the key K being employed for initiating the marking and spacing impulses. The Winding We of the receiving relay E may be connected in series with e, resistor Z3 and a battery Bi. The latter circuit is known as a biasing circuit. The telegraph circuit so far described is of well known type and in this circuit the relay T may be omitted if desired, the conductors L1 and L2 being then interconnected by the key K With the sparkkiller circuit bridging the lever of the key K and its marking Contact. To this telegraph circuit of well-known type a condenser C2 is added, this condenser being bridged across the contacts M and S of the relay T in accordance with this inventicn.

The operation of the circuit of Fig. 1 will now be described, assuming for the present that the condenser C2 is omitted as in the prior art, and that the line conductor L2 does not have grounded capacitance as represented by Co. If the key K is closed, the armature of the relay T will close its marking contact M. Current will then iiow from batteries B1 and B2, which are arranged to be series aiding, this current traversing the winding W1 of the receiving relay R and the resistor Z1. The armature of the relay R will then close its marking contact M to register a marking pulse. When the key K is subsequently opened, the armature of relay T will leave its marking contact M and will then close its spacing Contact S, thereby interrupting the iiow of current from batteries B1 and B2. The current in winding W1 of relay R will then decay to a zero value. The armature of the relay R will then travel to its spacing contactI S to register a spacing pulse.

The decay of current for the spacing pulse will generally occur at a substantially different rate from the rise of current for the marking pulse. The difference between the two rates of current variation is due to the impedance changes of the line circuit between the marking and spacing conditions, and is also -due to the presence of the spark-killer in the circuit. The condenser C1 of the spark-killer circuit will be charged by batteries B1 and B2 Whenever the armature of relay T is separated from its contact M. Condenser C1 will be discharged through resistor Zz when the armature of relay T rests upon its contact M.

Thus on initiating a spacing interval, current will flow through the line conductor La to charge and condenser C1.

condenser C1 for a time, and this current will gradually decay to zero, as is indicated at Il of Fig. 3 for the spacing interval D11. 'I'he length or duration or the spacing impulse recorded by relay R will hence be modified,i.e.shortened by the iiow oi' this charging current. The duration of the spacing pulse as recorded by relay R, is illustrated in Fig. 3 by the reference character D1. But the marking impulse will begin almost immediately aiter contact M of relay T is closed, i! the reactance of the circuit is small. The length of the marking pulse as recorded by relay R, is designated Dz in Fig. 3. The times during which the armature of relay T closes its spacing contact S and its marking contact M are also shown in Fig. 3, where they are designated D11 and D11. respectively.

It will be observed from Fig. 3 that although the marking and spacing intervals are intended to be substantially equal, the unsymmetrical operating current traversing the winding W1 of relay R results in a lengthening oi' the marking interval Dz and a shortening of the spacing interval D1 in the signals repeated by the relay R. This undesirable eiIect `is known as marking bias. The neutral telegraph circuit with its spark-killer circuit operates, as pointed out above, to establish a ilow of current for each marking signal and to interrupt the current by opening the line circuit for each spacing signal. Such a circuit commonly involves what is known as signal bias. On the other hand, in a polar type of telegraph circuit the marking and spacing intervals are produced by oppositely poled batteries, and there is, therei'ore, no signicant change in impedance between the marking and spacing conditions, and no such signal'- bias takes place. In polar circuits the wave shape is substantially symmetrical, i. e. the rate of growth oi' current is exactly or nearly the same as the rate of decay of current.

In accordance with this invention the advantages of the polar type of telegraph circuit above referred to may be obtained in a neutral telegraph circuit without actually having two 45 separate and distinct transmitting batteries.

This advantage may be obtained merely by connecting a suitable condenser, such as that designated Ca in Fig. 1, across the marking and spacing contacts M and S of the sending relay T.

When the condenser Cz is employed it will be seen that when the armature of relay T is on its contact S, the condenser C1 will be charged to a voltage equal to the sum of the voltages of the batteries B1 and B2. Likewise the condenser C1 of the spark-killer will be charged to this same voltage. When the armature oi' relay T moves to its marking contact M in response to a marking signal, current will iiow through the winding W1 of relay R to register a marking pulse, but con- 0 denser C1 will remain fully charged, except for the unavoidable leakage which for practical purposes is negligible. While contact M oi' relay T remains closed, the spark-killer condenser C1 becomes discharged through its own resistor Zz.

Just as soon as the armature of the sending relay T opens its marking contact M, the batteries B1 and B1 will begin charging condenser C1 over a circuit which includes the battery B1, the conductor L1, the resistor Zz, condenser C1, the line conductor La, the winding W1 of relay R, the resistor Z1, the battery Bz and ground. Much before the charge of condenser C1 is completed, the armature of relay T will touch its spacing contact S and condenser C2, being fully charged, will act to rapidly complete the charge on condenser C1. I! condenser C: is large compared to condenser C1, the charge on condenser Cn will not be much reduced by this process. The current ilowing in the line conductor La will immediately fall to a negligible value. Condensers C1 and C: will thus be charged fully to the voltage of batteries B1 and Bz by this current now. The presence of this small current flowing after the operation of relay R to its spacing contact will, of course, have no eilect upon the spacing signal reproduced by relay R. The important feature, however, is that the comparatively gradual decay of current experienced before condenser C: was

added to the circuit has now been changed to a comparatively rapid decay and the signals reproduced by relay R will be improved thereby.

Fig. 4 shows a graph of the operating current in the case in which the condenser C2 has been added to the circuit. It will be seen that the comparatively slow decay of current illustrated at 2| oi' Fig. 3 during the spacing interval is changed to a rapid decay, as shown at 24 and 25 of Fig. 4. The spacing and marking intervals during which the relay R registers the spacing and marking signals respectively are Vdesignated D1 and D1 in Fig. 4, and it will be observed that the disparity between these intervals in the signals registered by relay R is considerably reduced. Upon the addition ot the condenser Cz across the marking and spacing contacts oi' the relay T, the neutral telegraph circuit is thus converted in practical effect, so i'ar as the operation of the circuit is concerned, to the polar type of circuit with the accompanying improvement in transmission.

Condenser C2 is chosen large enough in capacity so that it will be able to complete the charge of condenser C1 of the spark-killer circuit when the contact S oi' relay T is closed without .itself dropping appreciably in voltage. In one arrangement tried out the condenser C1 was oi' 4 m. i'. capacity-16 times as large as condenser C1, which was V4 m. f. capacity. The resistor Zz was oi' 1,600 ohms. It was also found that the capacity of condenser C: could be varied over a wide range without appreciably ailecting transmission.

Ii desired, a resistor may be inserted in series with the condenser Cz to reduce the tendency of the circuit to oscillate and also to reduce any sparking which might exist when the armature of relay T closes its spacing contact S.

To recapitulate: The condenser Cz of large capacity is nrst charged to a voltage equal to that oi' batteries B1 and Bn which, for the sake of convenience, will be called the line or battery voltage. This occurs whenever the armatures of the sending relay T closes its contact S. The line or battery voltage is also applied to the smaller condenser C1 oi' the spark-killer circuit but the charging rate is somewhat held down by the resistor Zz which is interposed in the path of the condenser C1. When the armature of relay T later closes contact M, current will ilow through the winding W1 to register a marking pulse, but condenser C: will remain i'ully charged except for unavoidable leakage which, for practical purposes, is negligible. While contact M remains closed, the spark-killer condenser C1 becomes discharged through its own resistor Zz.

Just as soon as the armature o! the sending relay T opens its contact M, the line battery will again charge the condenser C1 to a voltage approaching that of the battery voltage. When the armature of relap T then closes its contact S, the

condenser C2 will rapidly complete the charge of condenser C1, through resistor Zz and because of its large relative size, the voltage of condenser C2 5 will not be much reduced. And while contact S remains closed, the voltage of condenser C2, which is approximately equal and opposite to that ofthe line battery, will fully oppose the line battery voltage and therefore no current will Flow through the winding Wiel" the receiving relay R. Hence the relay R will register a spacing signal. These conditions will be repeated again and again as the sending relay armature travels back and forth between its contacts.

In the circuit of this invention, the sparkkiller circuit of resistor Z2 and condenser C1 may be omitted if so desired. The spark-killer circuit may be omitted, for example, when arcing at the relay contacts is small or of no consequence. In that event when contact S of relay T is closed, the condenser C2 which hasA previously been charged to the line or battery voltage, will oppose the line or battery voltage and the receiving relay R will register a spacing signal. But when contact M of relay T becomes closed, the line battery current will energize the winding of relay R which will then register a marking signal.

The schematic circuit of Fig. l has been described as a one-way telegraph system for transmitting marking and spacing signals from the point where relay T may be located over line conductor Lz to a possibly different point where relay R may be located. However, two-way transmission may be accomplished by a circuit such as that illustrated in Fig. 2.

In Fig. 2, the batteries B1 and B2 are poled so as to be series aiding as in Fig. 1. The apparatus at the two ends of the line L3 are otherwise duplicates, the apparatus at station E being indicated 40 by reference characters which are primed with respect to the same apparatus at station D. it will be understood, of course, that the armature of relay T will be maintained at contact M when signals are to be transmitted from station D to station E, and that the armature of relay T at station D will be held at its contact M when signals are to be transmitted from station E to station D.

When signaling from station D to station E, the voltage applied to condenser C2 will oppose the voltages of batteries B1 and B2 taken together Whenever the armature of relay T closes its spacing contact S. A spacing signal will then be registered by both receiving relays R and R'. Similarly, the condenser C2 will have a voltage at charge which will oppose the total line voltage whenever the armature of relay T' closes its spacing contact S1 as when signaling from station E to station D. And in the circuit of Fig. 2, the spark-killer circuits Crand Zz and C1' and Zz' may be omitted if so desired. Furthermore, a single battery may be used in place of the two batteries shown.

It will be understood that any number of trans- 55 mitting (and receiving) relays may be added in series with each other for signaling between any nungber of stations. This series arrangement cannot be employed with the typical differential telegraph system which, as is well known, em- 0 ploysf'a circuit which connects oppositely poled batteries to the line for producing the marking and spacing signals. The advantages of the present invention are that the condensers C2, C2', etc. do not involve any battery Doling considera- 75 tions whatever, the circuit impedances are maintained substantially constant, and signal bias is substantially reduced or eliminated. In using the circuit of theinvention, however, the charges of condensers C2, C2', etc. will be somewhat dissipated after a long marking interval and the condenser charges must be restored before signal distortion will be eliminated.

The biasing circuit of the receiving relay, i. e. the circuit ci winding W2, resistor Z3 and battery Bg of Fig. l, for example, should preferably have a high resistance. it has been found that the circuit of the invention will operate very satisfactorily if the resistanceof the bias circuit is made at least as high as the resistance in the line or loop. A low resistance for the bias circuit will introduce considerable signal distortion which is clearly undesirable.

While this invention has been shown and described in certain particular arrangements merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organications without departing from the spirit oi' the invention and the scope of the appended claims.

What is claimed is:

l. in a neutral telegraph system, the method of signaling to a loop or line with a soiuce of voltage and a condenser charged to the voltage of said source, which consists in sending current through said loop or line from said source to produce one type of pulse therein, and then applying the voltage of the condenser to the loop or line to oppose `the voltage of said source and thereby suppress the iiow of current through said loop or line to produce a diierent type of pulse therein. v

2. In a neutral telegraph system, the method of signaling between two points with a source of voltage and a condenser charged to the voltage of said source, which consists in applying the voltage of said source between said points to send current therebetween, maintaining the condenser voltage substantially unchanged, and neutralizing the voltage between said points by opposing the voltage of said source by the condenser voltage to stop the flow of current between said points.

3. The method of sending signals in a telegraph system which consists in charging a condenser to a predetermined voltage, applying an equal Voltage to produce one type of signal, and opposing the applied voltage with the voltage impressed on the condenser to nullify the effective voltage to produce another type of signal.

4. 'Ihe method of signaling in a neutral telegraph system with a source of voltage and a condenser which consists in charging the condenser to the voltage of said source, applying the source of Voltage to the system to transmit current in accordance with a marking signal, and then applying the condenser to the system so that its voltage will oppose the voltage of the source and thereby suppress the flow of current in accordance with a spacing signal.

5. In an open-and-close telegraph system, a source of potential, a condenser, a line, a relay having two contacts between which said condenser is permanently connected, said line being connected in series with said source and the armature and one of the contacts of said relay, said condenser being eifectively connected both to said line and said source only during the time kwhen but one of the contacts of said relay is closed.

6. In a telegraph system, a sending device having a vibrating member and only two terminals between which said vibratory member may move, a source of voltage connected between said vibratory member and one oi its terminals, and a condenser permanently connected between both terminals o! said device.

'1. In a telegraph system, the combination of a sending armature which is movable between first and second contacts, a condenser permanently connected between said nrst and second contacts, a source oi' voltage, a load, said source being connected in series with said load and the armature and its nrst contact, and a spark-killer circuit connected between said armature and its rst contact.

8. In a telegraph system, the combination oi' a sending relay, a receiving relay, a source o! voltage, and a condenser permanently connected between the contacts of the sending relay, the source of voltage being connected in series with the receiving relay winding and the armature oi.' the sending relay and one of its contacts.

9. In a telegraph system, the combination of a sending relay, a receiving relay, a source oi voltage, a first condenser of large capacity connected across the fixed contacts of the sending relay, a spark-killer circuit including a second condenser of small capacity, the source of voltage being connected with the receiving relay winding and the armature and one of the contacts oi the sending relay, the spark-killer circuit being connected to the armature and the same contact of the sending relay.

10. In a telegraph system, the combination of a source of voltage, a member which is movable between two contacts, and two circuits containing capacitances of different magnitudes, the circuit of larger capacitance being connected between said two contacts, the circuit of small capacitance being connected between said movable member and one of its contacts, and a load connected between said source of voltage and said movable member and the latter contact.

1l. In a telegraph system, a source of voltage, a loop, a condenser which is normally charged to the voltage oi' said source, means for producing a marking impulse in said loop by connecting said source thereto, and means for producing a spacing impulse in said loop by connecting said source and said condenser to said loop so that the voltage of said condenser will oppose that of said source.

12. In a telegraph system, a source of voltage, a condenser, a loop, means for sending current from said source through said loop for producing one type of telegraph signal therein, and means for substantially reducing the current flowing from said source to said loop to produce another type of telegraph signal therein, said latter means including means to connect the condenser to said source through the loop so that the charge on the condenser will oppose the ow oi current from said source.

13. In a telegraph system, a relay, a sparkkiller circuit connected between the armature and one of the ilxed contacts oi.' the relay, and a condenser connected between both fixed contacts of the relay, the spark-killer circuit comprising a resistor and a second condenser connected in series.

` 14. A telegraph system comprising a line, a source oi voltage, a receiving relay, a sending relay, the line being connected in series with said source and the receiving relay winding and the armature and one oi' the fixed contacts of the sending relay, a spark killing circuit comprising a series connected resistor and condenser connected between the armature and the same contact of the sending relay, and a second condenser connected across both fixed contacts of the sending relay.

l5. In a telegraph circuit, a source of voltage, a transmitting relay having an amature and two contacts, a condenser, means for charging said condenser to the voltage oi' the source when the armature closes one of its contacts, the condenser charge remaining substantially unchanged after the armature leaves the latter contact, and means for transmitting a substantial current from said source when said armature closes its other contact.

16. In a neutral telegraph circuit, h source of voltage, a condenser charged to the voltage o! said source, a load device. means i'or producing a marking signal at said load device by allowing current to iiow from said source through said load device, and means for producing a spacing signal at said load device by opposing the voltage of the condenser against the voltage o! said source.

17. In a neutral telegraph system, the combination of a line over which marking and spacing signals are to be transmitted by the flow o! current or the absence o! current, respectively, the combination of a source of voltage, means for intermittently connecting said source to said line to transmit marking current thereover, a condenser, means i'or charging said condenser to the voltage ot said source, and means connecting said source and said condenser to said line so that both will oppose each other for conveying a spacing signal over said line.

18. In a telegraph circuit having an element movable between two contacts for opening the circuit to establish a spacing signal and ior closing the circuit to establish a marking signal, means for maintaining the impedance of the circuit substantially constant i'or the frequencies employed during signaling, said means comprising a condenser connected between the two contacts oi' said element.

19. In a telegraph circuit including a keying device having two flxed terminals, one terminal being contacted for opening the circuit for a spacing pulse, the other terminal being contacted for closing the circuit for a marking pulse, means for avoiding undesirable changes in impedance between the marking and spacing conditions, said means comprising a condenser permanently connected to the terminals of said keying device.

GORDON JOHN HARMS. 

